Plants are useful resources for producing a wide range of secondary metabolites to be used for medicines, agricultural pesticides, spices, pigments, food additives, cosmetics, etc. However, if a secondary metabolite is directly extracted from a plant, its content is low, and its productivity is highly varied depending on a cultivation condition or a part of the plant, which causes an unstable supply of the secondary metabolite. Further, while demands for secondary metabolites are increased in food, medicine, and cosmetic fields, supplies of secondary metabolites directly produced by cell culture are still limited. In order to solve such a problem, there have been various attempts to control a mass production process and a culture condition in a bio reactor capable of mass-producing secondary metabolites.
Mass production of secondary metabolites through plant cell culture has problems of instability of a culture cell strain, low productivity, and slow growth, mass culture, and the like. In order to overcome the problem of low productivity, conventionally, 1) manipulation of nutriments of a culture medium such as addition of sugars, nitrates, phosphates, growth regulators, and precursors, or the like, 2) optimization of culture environment such as a culture temperature, lighting, acidity of a medium, etc., 3) treatment of derivatives for increasing productivity, 4) cell membrane permeabilization and two-phase culture for effectively collecting of secondary metabolites, and 5) modification of genes involving biosynthesis of secondary metabolites and transfer of exotic genes have been used for increasing productivity of secondary metabolites. However, such methods can be limitedly used for specific cells or specific metabolites but cannot be generally applied to cell culture and secondary metabolites.
Meanwhile, a method for culturing cells is classified into a batch culture method in which a culture fluid and a cell are supplied once at the beginning and there is no more supply or removal of nutriments, and a continuous culture method in which a culture fluid is put in an incubator and a new culture fluid is supplied from the outside at a constant speed while the old culture fluid containing a cultured product is discharged to the outside at the same speed so as to continuously culture cells without lack of nutrients. The batch culture method is not suitable for mass production. Therefore, as one of the continuous culture methods, a perfusion culture method in which a cell is left in an incubator and a medium containing a product is continuously collected while a new medium is supplied has attracted attention. In this case, it is disclosed that cells and a medium are separated from each other by using ultrasonic waves. To be specific, by using an ultrasonic cell separator operated such that when cells start to be discharged to the outside of the cell separator after ultrasonic waves are irradiated, the irradiation of the ultrasonic waves is stopped, and the cells are returned to a bio reactor by applying a counter pressure with a pump, and then the ultrasonic waves are irradiated again, the cells and the medium are separated, whereby plant cells are cultured at a high density. However, in this case, the ultrasonic waves are used to separate the cells and the medium, but cannot much contribute to an increase in content of secondary metabolites of the cells. Further, it has been pointed out that necrosis of the plant cells is often caused by the ultrasonic waves.    Patent Document 1: Korean Patent Application No. 10-1997-0008119    Patent Document 2: Korean Patent Application No. 10-2000-0017570